1. Technical Field
This application generally relates a touch detection method and a touch detection apparatus, and more particularly, to a touch detection method and a touch detection apparatus for detecting a touch area and touch coordinates by detecting a touch signal.
2. Background Art
A touch screen panel is an input device that receives a user input based on contents displayed by an image display apparatus by touching the touch screen panel with a hand of a human or other touch means.
The touch screen panel is located in a front face of an image display apparatus and converts a contact position of the touch screen panel, at which the contact is made by a hand or other contact means, into an electric signal. Therefore, an instruction selected at the contact position is accepted as an input signal.
In general, the touch screen panel is implemented by a resistive method, an optical detection method, and a capacitive method for detecting a touch. A capacitive touch screen panel converts a contact position into an electric signal by detecting change in capacitance formed between a conductive detection pattern and nearby another detection pattern or a ground electrode when a hand or an object makes contact with the touch screen panel.
FIG. 1 is an exploded plan view illustrating an example of a conventional capacitive touch screen panel.
Referring to FIG. 1, a touch screen panel 1 includes a transparent substrate 2, and further a first sensor pattern layer 3, a first insulating layer 4, a second sensor pattern layer 5, a second insulating layer 6, and a metal interconnection 7 that are sequentially formed on the transparent substrate 2.
The first sensor pattern layers 3 may be connected in a row direction on the transparent substrate 2, for example, the first sensor pattern layers 3 may be provided in a regular pattern having a plurality of diamond forms aligned. The first sensor pattern layers 3 located on a single row with the same Y coordinate are connected to each other, thereby forming a plurality of Y patterns, and the first sensor pattern layers 3 are connected to the metal interconnection 7 in units of rows.
The second sensor pattern layers 5 may be connected in a column direction on the first insulating layer 4, for example, the second sensor pattern layers 5 may be provided in a regular pattern having a plurality of diamond forms in the same manner as the first sensor pattern layers 3. The second sensor pattern layers 5 located on a single column with the same X coordinate are connected to each other, and alternatingly disposed with the first sensor pattern layer 3 without overlapping the first sensor pattern layers 3. In addition, the second sensor pattern layers 5 are connected to the metal interconnection 7 in units of columns.
The first and second sensor pattern layers 3 and 5 may be formed of a transparent conducting material, such as indium tin oxide (ITO), and the first insulating layer 4 may be formed of a transparent insulating material.
Each of the sensor pattern layers 3 and 5 is electrically connected to a driving circuit through the metal interconnections 7.
When a finger of a human or a contact means makes contact with the touch screen panel 1, a change in capacitance based on a contact position is transmitted to the driving circuit through the first and second sensor pattern layers 3 and 5 and the metal interconnection 7. The transmitted change in capacitance is converted into an electric signal by X and Y input processing circuits so that the contact position is recognized.
However, the touch screen panel 1 needs to be additionally provided with ITO patterns formed on the respective sensor pattern layers 3 and 5, and the insulating layer 4 needs to be provided between the sensor pattern layers 3 and 5, which causes the thickness of the touch screen panel 1 to be increased.
Since the conventional touch detection is achieved by accumulating a plurality of times of changes in the capacitance that arises to a small degree, the capacitance change needs to be detected at a high frequency, and thus a complicated operation and statistical processing processes are required.
In addition, in order to sufficiently accumulate the change in capacitance for a predetermined period of time, a low resistance needs to be maintained and thus a metal interconnection is required. Such a metal interconnection causes a bezel at a rim of a touch screen to be thicker, and requires an additional mask process.
FIG. 2 is an equivalent circuit for detecting a touch at the time of occurrence of a touch.
FIG. 2 shows an equivalent circuit for a capacitive touch detection method in which a touch is detected by measuring a level shift.
Referring to FIG. 2, a finger makes contact with a sensor pattern, Cvcom, Cdrv, Cp, Ct, and so on are generated. Since the touch screen panel recognizes a touch by detecting the amount of change in Ct, Cp, Cvcom, and so on act as noise.
In addition, the touch screen panel applies a clock signal, such as an alternating voltage Vdrv, to the sensor pattern and applies a variation detected by the sensor pattern, that is, an output of the sensor pattern to an input of an Analogue to Digital Converter (ADC), to acquire an output value. Accordingly, a voltage variation at an output end of the sensor pattern at the time of occurrence of a touch on the touch screen panel is determined by Formula 1 below.
                              Δ          ⁢                                          ⁢                      V            o                          =                              ±                          (                                                V                  drvH                                -                                  V                  drvL                                            )                                ⁢                      (                                          C                drv                                                              C                  drv                                +                                  C                  p                                +                                  C                  t                                                      )                                              [                  Formula          ⁢                                          ⁢          1                ]            
ΔVo is a voltage variation at a sensor pattern, VdrvH is a high level voltage of an alternating voltage Vdrv, VdrvL is a low level voltage of an alternating voltage Vdrv, Cdrv is a driving capacitance, Cp is a parasitic capacitance, and Ct is a touch capacitance.
Since Ct is placed at a site of a denominator in Formula 1, ΔVo is increased with increase of Ct. However, the increase in ΔVo does not have a perfect linearity.
The difference of voltage variations ΔVo before and after a touch corresponds to a touch area, and as seen in FIG. 2 that touch coordinates are obtained by use of the touch area, touch coordinates are more easily obtained if the linearity is ensured.
To this end, a table may be configured to map ADC output values to Ct values in one to one correspondence, and the Ct value may be obtained by look-up of ADC results. However, since the Cp values are different at respective touch nodes, the table needs to be configured for each node and the size of a memory consumed to configure the table is increased, which causes drawbacks in terms of system performance and cost of the overall system. In addition, since the time taken to configure the table is long, the driving time of the system may be delayed.